1. Field of the Invention
The invention relates to the field of transmitting structured datasets between client and server means.
2. Discussion of the Related Art
A structured dataset in particular may be a web page composed of a base file and a number of subfiles, as diagrammatically shown in FIG. 2. The web page illustrated is described in the base file x0 (for instance, in the Hypertext Markup Language, HTML), and the base file may contain references to other objects potentially needed for presenting the web page. Such additional objects especially may exist in the form of files which then are referred to as subfiles (to the base file). FIG. 2 shows eight such objects (subfiles) x1, . . . , x8. The objects may be text objects, picture objects, graphics, audio, video objects, etc. and furthermore they, too, may contain structured information (e.g. in HTML) which in turn likewise may include references to further subfiles, just like the base file. This nesting may be continued recursively. The number of subfiles and their nesting depth per web page may be arbitrary as needed and may be different for different sites.
A prior art method of this kind is described in DE 100 39 901. Moreover, DE 100 39 901 describes a method which, by resorting to a client proxy means and a server proxy means, allows much faster transmission through transmission networks in which, for example, transmission delays are great. Such transmission networks with disadvantageous great delays in transmitting, for instance, may be satellite networks.
An example of the prior art which existed prior to document DE 100 39 901 and was critically assessed in that publication is illustrated in FIG. 3. A client means (such as a web browser) accesses a server means (such as a web server) through two simple proxy means e.g. on the internet, for instance, in order to fetch a web page structured, for example, as illustrated in FIG. 2. Communication between client and server means takes place especially through a network having a high transmission time (e.g. a satellite network). When accessing the web page, the client means first sends a request for the base file x0 and then receives it in a first reply from the server means. Thereupon, the client means analyzes the base file x0 and finds a number of embedded objects x1, . . . , x8 which it subsequently fetches in two rounds from the server means. Due to the high transmission time within the network, the operation from the first inquiry for the web page to the complete presentation in the client means takes very long.
According to DE 100 39 901 this state of the art is improved by introducing a distributed proxy consisting of a client proxy means and a server proxy means, as illustrated in FIG. 4. Here, both the client and the server proxy means may be placed so as to enclose the network with great transmission delay. As may be gathered from FIG. 4 (and described in detail in DE 100 39 901), the efficiency in accessing structured datasets is improved by a request (A) which causes the analysis of a base file x0 (and corresponding subfiles) to be undertaken additionally (C) in the server proxy means after the base file has been received (B) from the server means and before, during, or after it is forwarded (D) to the client proxy means. The server proxy means independently demands (E) the objects thus located (in this example subfiles x1, . . . , x8) from the server means, and the objects obtained from the server means likewise are forwarded (F) to the client proxy means, even if they have not yet been asked for. The objects (files, subfiles) received from the server proxy means are buffered in the client proxy means and, thereafter, any requests from the client means for these objects are answered (G) out of the memory means. This way of proceeding will be referred to below as “prefetching” since subfiles or objects are prerequested from a server means.